HEREDITY OF PIGMENTATION 165 
lateral line with the extremes at 21 and 34; while ten of the pure 
form averaged 18.6 with extremes at 3 and 29. In this series 
the F. heteroclitus egg hybrids hatched at the same time as the 
pure F. heteroclitus so that these comparisons were made at the 
same age as well as the same stage and the difference in favor of 
the hybrids cannot be due to their greater age. 
In the F. majalis egg hybrids the black chromatophores on the 
lateral line behaved quite similarly to those of the F. heterocli- 
tus egg hybrid. But as these hybrids usually never do hatch a 
precise determination of the hatching time could not be made. 
We have then so far as this character is concerned a well marked 
difference between the two species at the time of hatching and 
an incomplete dominance of the F. heteroclitus condition in the 
hybrids; but since the stages before and after hatching have not 
been sufficiently studied it cannot be told whether both species 
go through exactly the same series of changes, merely differing 
in their rate, or to what extent the hybrids are intermediate 
between the two pure forms. 
6. Distribution of yolk chromatophores 
At the time of their first appearance both kinds of yolk chroma- 
tophores in the pure F. heteroclitus and the F. heteroclitus egg 
hybrids were found to be distributed over the whole surface of 
the yolk, and the region opposite to the embryo had quite as 
many or nearly as many chromatophores as any other region. 
In the pure F. majalis, on the other hand, almost the whole of 
the yolk hemisphere opposite to the embryo was free from chro- 
matophores; and it took a number of days before the migration 
of pigment cells into this region became noticeable. The F. 
majalis egg hybrids presented an intermediate condition, for most 
of them had a small chromatophore free area in the region opposite 
to the embryo, and the others had fewer chromatophores than 
usual in this region. Figs. 11 and 12 show something of the 
differences between these last twoforms. Later on the migration 
of chromatophores filled these empty areas with pigment cells 
and obliterated the difference between the various forms. 
